1. Field of the Invention
The present invention is directed to a selective permeable membrane for separation of a liquid solution, and more particularly to such a membrane adapted in use to selectively separate a particular volatile component from its liquid solution containing another volatile component, for example, to separate the water from a water-alcohol mixture solution.
2. Description of the Prior Art
In order to separate a liquid solution such as a water-alcohol solution, it has been proposed to use a selective permeable membrane particularly suitable to a pervaporation method in which the membrane is in contact with the liquid solution for separation of the liquid solution. Included in the membrane for separation of water-methanol mixture is a cellophane membrane as proposed in the article "Japanese Polymer Science Symposium, No. 41, 145" in 1973, and a graft polyvinyl alcohol membrane as proposed in the article "Japanese Polymer Science Vol. 26, 3223" in 1981. Further, Japanese Patent Publication (KOKAI) No. 62-4407 discloses a chitosan-vinyl monomer membrane for separation of water-ethanol mixture, and Japanese Patent Publication (KOKAI) No. 62-7403 discloses a chitosan salt membrane for separation of water-alcohol mixture.
Unfortunately, these membranes have been found to be insufficient in its separation efficiency and failed to come into industry practice. The separation efficiency of the membrane can be evaluated in terms of a separation factor .alpha., which indicates that the membrane allows a particular component of the liquid solution to selectively permeate therethrough when .alpha. being greater than 1 and indicates a greater separation efficiency with increasing value of .alpha., as discussed hereinafter. The above membranes without chitosan show a separation factor only in the order of several tens and even the membranes including chitosan cannot have the separation factor increased to a sufficient level for commercial practice.